Vacuum bleeding hydraulic brakes?

Steinar

Steinar

Member
Hi!

I know my A should not have had hydraulic brakes, but I also know my A is not the only one with this setup. But one thing is a bit special on mine, instead of modifying the rear 46 - 48 brake shields, they are mounted up side down. Which make them a direct bolt on. This is not a result of my brain work, I just bought it this way, and now I am trying to restore the whole system to bring the car back out on to the road again, after maybe as much as 20 years standing still. Well, I put everything back in place, new master and new wheel cylinders. But I cannot get the air out of the system.
I've been bench bleeding the master, no sign of air there. So I feel pretty sure the problem is my rear cylinders, since bleeder screw is now at the bottom of the wheel cylinder, not at the top where it obviously should have been. So my question is, would a vacuum bleeding system be able to suck this air out, or should I go the hard way and do some cutting and welding mods to the brake shields? I sure hope that would not be necessary, the car has been run with this setup earlier. I also read a comment, I think on H.A.M.B somewhere, where this setup was described in an earlier Hot Rod Magazine.
I have heard some people telling they sometimes had to take the shields off the axle and let them lay down flat while bleeding. Doesn't sound right to me, would make a lot of stress on the brake tubings..

Is Vacuum bleeding the way to go, or doesn't it make much difference?
Any comments appreciated!


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fordgarage said:
...It was no problem to pressure bleed, one cylinder at a time...[/IMG]
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If you say it, I believe it, Vince, but your experience is unusual. Most people have Steinar's problem, with the top half of the cylinder remaining full of air that has no incentive to go the bottom of the cylinder, no matter how much pressure or vacuum is applied.

Removing the backing plates temporarily is one solution. Another slightly easier but potentially messier solution is to remove the forward shoe (on the right in Vince's photo since it is upside down). Pull the dust boot and piston, and allow the seal to come out of the bore at a slight angle so there is a small gap at the top. Have a helper SLOWLY AND GENTLY work the pedal to evacuate air, pushing the seal back into full contact during the pedal return stroke to prevent sucking air back into the cylinder.

Joe
 
Very interesting! That seems to be the exact same setup! But I've been pouring 3 liters with brake fluid through the system, no air bobbles to see, but after finished bleeding, always the same, first pedal goes to the floor. The next jump on the pedal gives a rock solid one. My new mastercylinder looks pretty much the same as the old one, and this is a very common mastercylinder, used on a whole lot of different American built cars, among them also Ford. I was told. I know the problem could occur if the piston inside was not able to move enough fluid, but it doesn't seem to be any differences between them..
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An old trick to bleed a cylinder with a broken bleeder screw is to just remove the outer dust shield and pop out the piston.. Then slip a about a .010" feeler strip over the top side of the cup/seal.. Wait for the fluid to start running clear and then button it back up..
 
Could you swap the wheel cylinders to the opposite sides, that way the line
would be going in the bottom and the bleeder would be on the top.
 
Bob C

That was exactly what I had in mind this morning. I took everything apart, just to discover they were not symetrical, it didn't work out..
- Great minds think alike!
 
Steinar said:
Bob C

That was exactly what I had in mind this morning. I took everything apart, just to discover they were not symetrical, it didn't work out..
- Great minds think alike!
Click to expand...

If you're willing to do a bit of modification to the backing plate, they will swap from side-to-side.
 
Fordgarage, that is how I did it. But I can assure you I've been doing more than a couple of rounds around the car. I did put almost a gallon with new fresh fluid through the system. It is no leak to see. No bubbles visible when bleeding, two weeks since last time I saw one! I'm afraid the rear wheelcylinders are holding the air in the top of the chamber inside the cylinder. Air always want to go up, when in fluid, and pressurebleeding doesn't seem to change that. I had hoped vacuum bleeding maybe would have turned out better, sucking out the air together with more fluid coming down the tube. But I think I have learned here that this construction maybe is not the best one. It's kind a hard to fight the laws of nature. I don't know how they bled this thing when it was built, maybe they just, like you, had more luck than what I have. Or maybe they turned the car upside down, what do I know :confused::D
I will think about what to do over the night, right now I feel very attracted to mrtexas' ideas, even though I also feel pretty sure JoeWays prescription also would work out fine. But like he said, a bit more messy. In the long run, I think I probably would be happier with the cylinder on top. Gives very easy maintenance.

Thanks to all of you! For good ideas and pictures!
I'm very impressed how fast things are working out here!

Steinar
 
BillLee/Chandler said:
If you're willing to do a bit of modification to the backing plate, they will swap from side-to-side.
Click to expand...

Yes, I know, I was very close to start doing that earlier today, when I decided to first give it a try at Fordbarn. But the way mrtexas does it seems to be a easier way out, less modifications necessary, and when all comes to all, I don't really need to have'em down there. They just happened to be down there when I bought the car..
 
Steinar said:
Yes, I know, I was very close to start doing that earlier today, when I decided to first give it a try at Fordbarn. But the way mrtexas does it seems to be a easier way out, less modifications necessary, and when all comes to all, I don't really need to have'em down there. They just happened to be down there when I bought the car..
Click to expand...

Ideas actually came from Dave Wilton, former owner MT Car Products.
 
Interesting, I've also been thinking about that, let the air go out through the line-nut connection. But since this one is located about at the middele of the chamber, I was thinking I would do better, but not fully good.
I also liked the upsidedown construction in the way it was a direct bolt on, not in need of any modifications. Generally I don't like to cut in old car parts and change them unless I have to.
But I have now been working on this thing for two weeks with no progress. Could it be that my cylinders are a bit different on the inside, making them more difficult to bleed when upside down? Bought them at SoCalSpeed Shop, but they were imports...?
 
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fordgarage said:
I have bled these upside down brake cylinders on a few occasions with absolutely no difficulty, so I am having a hard time understanding what might be fighting you, other than an air leak elsewhere.
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Did you always have to bleed them through the line-connection, or was this not typical when bleeding those upsidedown cylinders?
 
An old mechanic told me his proceedure it is as Vince mentioned. I use a squirt oil can the type with the long tube. Force a clear plastic tube unto the long tube. Push the other end onto the bleeder Take the cap off the master cylinder. Loosen the bleeder and pump away. Works for me. Also use silicone brake fluid. My cylinders don't freeze up anymore. Tony
 
Steinar said:
...The next jump on the pedal gives a rock solid one.
Click to expand...

If you get a good firm pedal on the second pump, then you probably have an adjustment problem rather than an air problem. The old Lockheed brakes can be tricky to get adjusted properly.

Joe
 
I agree with JoeWay. If you get a hard pedal on the second pump, there's no air in the cylinders. Air makes the pedal spongy - every time you press it. You need to spend more time adjusting the brakes.
 
I've done it several times exactly the way JoeWay suggests in #3. Anytime I get a car with a frozen bleeder and can't get the bleeder free, I also do it this way.
 
Maybe I didn't make my statement very clear, I guess thats a problem I have.. All you have to do is remove one wheel cylinder piston leaving the cup in place.. Insert a thin [about .010"] feeler strip between the top/high side of the cup and cylinder bore.. Walk away for awhile and residual line pressure will fill the cylinder and push the air past the feeler strip.. Once the fluid starts running out of the cylinder, down the backing plate and all over the garage floor, the cylinder is bled and the piston can be re-installed..
However, as has been said, the shoes should be somewhere near proper adjustment or the first pump of the pedal will just be used to push the shoes 'way out' in an attempt to find the drums.. If the pedal is 'hard and firm' then the air has been removed..
 
Steinar said:
Very interesting! That seems to be the exact same setup! But I've been pouring 3 liters with brake fluid through the system, no air bobbles to see, but after finished bleeding, always the same, first pedal goes to the floor. The next jump on the pedal gives a rock solid one. My new mastercylinder looks pretty much the same as the old one, and this is a very common mastercylinder, used on a whole lot of different American built cars, among them also Ford. I was told. I know the problem could occur if the piston inside was not able to move enough fluid, but it doesn't seem to be any differences between them..
picture.php
Click to expand...
My guess is that your problem is because your master cylinder piston is too small for the wheel cylinders. Check the diameter. Since you are not running a dual master cylinder why didn't you use the '39 to '48 master cylinder?

Charlie Stephens
 
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